Permanent magnet system for focusing an electron beam



April 27, 1965 R. STOCK 3,181,042

PERMANENT MAGNET SYSTEM FOR FOCUSING AN ELECTRON BEAM Filed April 30,1962 United States Patent 3 Claims. ci. 317-200 The invention disclosedherein is concerned with a permanent magnet system for focusing at leastone electron beam over an extended path, especially for use inconnection with travelling field tubes, wherein soft iron parts whichare operative to magentically connect the poles of the permanent magnetsare provided with bores formed therein for receiving the dischargevessel. The particular feature which is characteristic of the inventionresides in making the magnet system separable along a symmetry axiswhich extends through the bores.

It is known to produce, for the focusing of the electron beam in atravelling field tube, interiorly of the discharge vessel either ahomogeneous magnetic field or a magnetic field alternating in directionalong the dischargepath. In a system for producing a homogeneousmagnetic field, the magnet poles are for the homogenizing of this fieldinterconnected by soft iron cylinders. The bore of the soft ironcylinder is thereby so dimensioned that the discharge vessel can bedisposed inside of the cylinder. A permanent magnet system havingmagnets which extend with their magnetizing direction axiallysymmetrically to the electron beam in a plane perpendicular to the beamand along such beam, has been found particularly advantageous forproducing a directionally alternating magnetic field. Identical poles ofthe permanent magnets are thereby in electron radiation directionalternately serially connected by pole pieces which have respectively acentral bore formed therein for receiving the discharge vessel. Thediameter of the bores formed respectively in the pole pieces or in thesoft iron cylinder of the indicated prior permanent magnet systems, isso dimensioned, that the tube can be exchangeably inserted into thebores.

The bores should be as small as possible so as to obtain a magneticfield which is along the axis of the electron beam as strong aspossible. The tube is therefore inserted into the system with itsthinner end. This thinner end is in the known travelling field tubesusually the end at which is arranged the collector. The other end of thedischarge vessel, in which is disposed the electron gun, has a diameterwhich exceeds that of the central part thereof which contains the delayline. However, in the case of tubes of higher capacity, the diameter ofthe collector exceeds that of the central part of the tube. Accordingly,upon using a permanent magnet system for focusing the beam of suchtubes, the bore in the soft iron parts of the magnet system must belarger than the diameter of the part of the discharge vessel in which iscontained the delay line. It follows, therefore, that magnets with veryhigh magnetic energy content are required for producing strong magneticfields along the radiation axis.

The object of the present invention is to provide a permanent magnetsystem for travelling field tubes, especially travelling wave tubes,wherein the bores have a smaller diameter than would be necessary forpassing the relatively thick end of the travelling wave tube to beinserted therethrough.

It is in accordance with the invention proposed to realize this objectin connection with a permanent magnet system for focusing along anextended path, at least one electron beam, especially in a travellingfield tube, wherein bores for receiving the discharge vessel areprovided in the soft iron parts which interconnect'mag-neticallythepoles of-the permanent-magnets which are adjacentthe electron beam, tomake the magnet system :separ able along a symmetry axis which extendsthrough-ther-axis ofithe bores.

.Furtherdetails of theinventionwilhnow be-described with reference tothe-accompanyingdrawing.

FIG. 1 shows in xschematic :manner a separable 1 permanent-magnetsystemfor producing a directionally-a1- -ternating magnetic field; I

FIG. Z-indicates in-schematic-manner, for use with the permanent magnetsystem of- FIG. 1, a-waveaguide which may likewise be separable; and

FIG. 3 represents in schematic sectional view part of the permanentmagnet system of FIG. 1 with a travelling field tube extending throughbores formed in the soft iron members.

Referring now to FIG. 1, numerals 1, 2, 3, 4 indicate magnets which arein known manner arranged axial symmetrically to the electron beam so asto form the sides of a square, with identical poles abutting at thecorners of the square. Oppositely disposed corners with identicalpolarity are, in planes extending perpendicularly to the electron beamaxis, alternately interconnected by means of soft iron pole pieces suchas indicated at 5, 6, 7, 8. All pole pieces are provided with a centralbore 9, such bores being axially aligned for receiving the dis chargevessel.

The permanent magnet system shown in FIG. 1 is in accordance with theinvention split and separable along the dash lines 10. The system thuscomprises two portions between which can be inserted the central part ofthe discharge tube.

In the event that coupling and uncoupling wave guides are to be includedin the magnet members of a permanent magnet system made in accordancewith the invention, such wave guides can likewise be made so as to beseparable. FIG. 2 shows as an example a rectangular wave guide 11 whichis separable along the dash line 12. As will be seen, the separationline leaves the field pattern, for example, of the H -wave, undisturbed.The lines 13 indicate the high frequency currents of the H wave.

A part of the permanent magnet system of FIG. 1 is shown in FIG. 3 insectional view in combination with part of a travelling field tube, inorder to further explain the advantages obtained by the invention. Sincethe magnet system can be opened along the line of separation indicatedin FIG. 1, the pole pieces 5, 6, 7 and 8 can be brought into positionsdirectly adjacent to the central part of the discharge tube 14 whichcontains a delay line (not shown), despite the larger diameter of thecollector 15.

The invention is not inherently limited to details shown and describedherein. The invention is particularly likewise applicable in connectionwith a system comprising ferrite rings or in connection with a permanentmagnet system for producing a homogeneous magnetic field.

Changes may be made within the scope and spirit of the appended claimswhich define What is believed to be new and desired to have protected byLetters Patent.

I claim:

1. A permanent magnet system for focusing along an extended path atleast one electron beam, particularly for use in connection with atraveling field tube which is of greater thickness at the end portionsthereof than at the intermediate portion thereof, comprising permanentmagnets and soft iron parts magnetically connecting poles thereof,extending such poles toward the electron beam, said soft iron partshaving bores formed therein for receiving the relatively thinintermediate portion of such a tube, which bores are smaller in diameterthan the end ing such intermediate portion. 7

portions of such a tube, said magnet'system being split to form twoparts which are separable along a symmetry plane extending through theaxis of said bores for receivdistribution, comprising permanent'magnetsarranged axially symmetrically with respect to and extending along saidaxis, and having pole pieces which are in the axial directionsuccessively disposed for reception of such a tube, said pole piecesalternately magnetically interconnecting identical poles of oppositelypositioned permanent magnets, said magnet system being split in a planeextending along the longitudinal axis of mutually aligned succesa a, a a

3. A permanent magnet system according to claim 2, wherein said magnetsystem has Wave guides built thereinto respectively for the coupling anduncoupling of high frequency energy, said separation plane extendingthrough wall parts or" said Wave guides which are free of the flow Oftransverse CUIIGI'ltS.

'Reierences @itetl by theExanriner UNITED STATES PATENTS 2,791,718

JOHN F; BUnNs-Primar Examiner.

sively disposed pole pieces, so as to form two parts abut- 15 EpJAMESSAX, Examiner;

tingalong such plane and being separable therealong.

5/57" Glass mm- 317 200 2,956,193 1 0/60 Dewitt. -3'15-3.5

1. A PERMANENT MAGNET SYSTEM FOR FOCUSING ALONG AN EXTENDED PATH ATLEAST ONE ELECTRON BEAM, PARTICULARLY FOR USE IN CONNECTION WITH ATRAVELING FIELD TUBE WHICH IS OF GREATER THICKNESS AT THE END PORTIONSTHEREOF THEAN AT THE INTERMEDIATE PORTION THEREOF, COMPRISING PERMANENTNAGNETS AND SOFT IRON PARTS MAGNETICALLY CONNECTING POLES THEREOF,EXTENDING SUCH POLES TOWARD THE ELECTRON BEAM, SAID SOFT IRON PARTSHAVING BORES FORMED THEREIN FOR RECEIVING THE RELATIVELY THININTERMEDIATE PORTION OF SUCH A TUBE, WHICH BORES ARE SMALLER IN DIAMETERTHAN THE END PORTIONS OF SUCH A TUBE, SAID MAGET SYSTEM BEING SPLIT TOFORM TWO PARTS WHICH ARE SEPARABLE ALONG A SYMMETRY PLANE EXTENDINGTHROUGH THE AXIS OF SAID BORES FOR RECEIVING SUCH INTERMEDIATE PORTION.